Off-centered Pb Interstitials in PbTe

The nature of off-stoichiometry of PbTe has not been fully understood yet though many studies existed by investigating its intrinsic defects. We reinvestigated the formation of intrinsic defects of PbTe by DFT study. From this, Te vacancy (V_Te) was the major defect under Pb-rich condition. Due to experiments that reported the increase of the lattice parameter as the Pb excess content grew up, a controversy between the DFT and the experimental results existed since the existence of V_Te could not explain the volume increase. So we assumed Pb interstitial (Pb_Int) as the major defect in PbTe instead V_Te because it not only exhibited the second-lowest formation energy, but also could be responsible for the lattice parameter increase. From this, all possible Pb_Int positions in PbTe were first investigated to understand its off-stoichiometry. As a result, we found new stable positions of Pb_Int other than the conventional one at the subcubic center. Moreover, among the various locations, Pb_Int toward the nearest Te and Pb dimer with Pb_Int were the ground and a metastable state. Finally, we believed that the many local minima of Pb_Int might be responsible for the off-stoichiometry of PbTe during the sintering of thermoelectric PbTe.